The widget:atts directive in the fields.ini file allows any arbitrary HTML attributes to be added to any of the fields. It may also be used to specify javascript event handler functions that the widget should call upon the specified event. In particular, here are some examples of possible widget:atts directives:
This directive sets the length of the input area a text box field, but it does not limit the number of characters that can be entered. For example: widget:atts:size = 50
This directive specifies the style (font-size, font-family, etc.) for the field. For example: widget:atts:style = "font-size: 24pt; font-family: Apple Chancery"
This directive will cause the specified javascript function to be called with the value of the field whenever its value is changed (i.e. when you change the field and tab out of it). For example: widget:atts:onchange = "doJsFunction();"
This directive will cause the specified javascript function to be called with the value of the field whenever it is clicked. For example: widget:atts:onclick = "doJsFunction();"
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Helpful tutorials
See the bottom of this page in the Getting Started tutorial for more details on the basic directives above: